Biologists have unravelled why deep diving mammals such as sperm whales can hold their breath for over an hour when diving for food – they have electrically charged proteins in their blood.

The researchers believe the finding may explain why some sea mammals are able to make such long underwater dives while other mammals can only hold their breath for a few minutes.

Sperm whales make some of the longest dives achieved by mammals, with some lasting up to 90 minutes, while dolphins and other whales can stay underwater for 20 minutes.

The longest time a human has held their breath for under water is 19 minutes – set by a Swiss freediver called Peter Colat.

Scientists at the University of Liverpool analysed a distinctive molecular signature of a protein called myoglobin, which binds oxygen in blood, from 100 different mammal species.

They found that in deep diving mammals like sperm whales it became more electrically charged.

This charge causes the proteins to repel each other, preventing them from forming clumps that can impede their ability to carry oxygen.

The scientists say this means sperm whales can pack more myoglobin into their muscles without harming their efficiency.

Dr Scott Mirceta, one of the biologists behind the research, said: "Our study suggests that the increased electrical charge of myoglobin in mammals that have high concentrations of this protein causes electro-repulsion, like similar poles of two magnets.

“This should prevent the proteins from sticking together and allow much higher concentrations of the oxygen-storing myoglobin in the muscles of these divers."

Myoglobin typically gives meat and blood its red colour is found in extremely high concentrations in the muscles of mammals that hunt in the deep ocean. This causes their muscles to be almost black in colour.

The research, which is published in the journal Science, could also help to improve understanding of human diseases where proteins clump together, such as in Alzheimer’s Disease.

It may also help the development of artificial blood substitutes.

Dr Michael Berenbrink, who led the study at the University of Liverpool’s Institute of Integrative Biology, said it was also allowing scientists to trace the evolutionary history of mammals.

He said: "We studied the electrical charge on the surface of myoglobin and found that it increased in mammals that can dive underwater for long periods of time.

“We were surprised when we saw the same molecular signature in whales and seals, but also in semi-aquatic beavers, muskrats and even water shrews.

"By mapping this molecular signature onto the family tree of mammals, we were able to reconstruct the muscle oxygen stores in extinct ancestors of today's diving mammals.

“We were even able to report the first evidence of a common amphibious ancestor of modern sea cows, hyraxes and elephants that lived in shallow African waters some 65 million years ago."